Regions

Regions are two-dimensional filters that can be used to
include or exclude data from a given data file. They may be
applied to any column in a file (time, spatial,
etc.). Regions can be read and written by the ds9 imaging
tool and read by CIAO tools (e.g. using a region with
dmextract to extract just the source
photons).

Regions are made up of a number of shapes that are listed
in the dmregions ahelp page. The
shapes can either be inclusive or exclusive and can be
combined using either a boolean AND or boolean OR operation.

For more information on creating and using regions, see the
following threads: